Techniques to generate two-dimensional (2D) dense assemblies or periodic arrays with feature size of 20 nm or smaller in a substrate are in great demand for pattern miniaturization in applications such as bit patterned media, logic devices for information processing, nanosensors, and nanoplasmonics. Available techniques include electron beam (or e-beam) lithography and block copolymer lithography.
E-beam lithography uses a focused electron beam to fabricate individual nanoscale features on a resist, which is then developed and etched to transfer the pattern into a substrate. However, patterning a single magnetic hard disk may require about a week, and so this technology may have to be combined with nanoimprint technology to be economically viable. Achieving feature sizes less than 20 nm may be challenging due to forward scattering of electrons in the resist. Attaining high packing densities may also be difficult.
Alternatively, block copolymers self-assemble into polymer domains that can be combined with conventional lithography to make patterned arrays and then transferred into underlying substrates. However, there are stringent requirements on the energetics of surface and interface to control the morphologies of block copolymer self-assembly, making it increasingly difficult to scale to sizes below 20 nm. Mixtures of spherical, lamellar, and cylindrical (both perpendicular and parallel to the substrate) morphologies are often obtained.